The purpose of the proposed investigation is to determine 1) the acute behavioral and anatomical consequences of lesions to the spinal cord at various ages and 2) the behavioral and morphological events which lead to recovery from the deficits. Specifically, we propose 1) to define the sequence of behavioral steps which lead to the recovery of locomotor behavior as a result of thoracic hemisection in rats at birth, 21 days of age and in adulthood, and 2) to demonstrate through the use of behavioral techniques the region or system which mediates that recovery. In addition, we propose 3) to demonstrate some of the morphological events which may be associated with the behavioral recovery. These events will be examined both in the region below the lesion and in the region of the red nucleus. The behavioral techniques will include conditioning and reflex testing. The anatomical techniques will include degeneration stains, horseradish peroxidase, Golgi impregnation and the Rasmussen stain. We will attempt to correlate the time course of the recovery of locomotor behavior with the morphological events which occur as a result of the damage. These correlations will contribute to our understanding of the behavioral recovery so that we will be able to formulate new and/or reinforce old hypotheses about recovery after CNS damage. In time, these hypotheses will be tested and the results used to develop a rational approach to enhance recovery of function.